Many voltage blocks are illustrated and described in the prior art. There are, for example, the voltage blocks illustrated and described in U.S. Pat. Nos. 4,878,622; 4,982,903; 5,033,942; 5,154,357; and 5,193,750, and the references cited in those patents, particularly including U.S. Pat. Nos. 1,655,262; 2,547,440; 2,673,232; 3,098,890; 3,122,320; 3,291,889; 3,893,620; 3,933,285; 3,934,055; 4,017,029; 4,020,866; 4,085,892; 4,275,834; 4,313,475; 4,383,644; and, 4,413,788, and U.K. Patent Specifications 1,393,333 and 1,478,853. Also of interest are U.S. Pat. Nos. 2,814,551; 2,921,604; 3,419,827; 3,450,092; 3,838,946; 4,030,860; 4,232,055; 4,304,252; 4,381,180; 4,386,888; 4,515,516; 4,552,334; 4,741,673; 4,792,092; 4,879,137; 4,881,688; 4,884,745; 4,932,589; 4,962,724; 5,078,168; 5,094,389; 5,096,126; 5,102,045; 5,102,046; 5,105,851; 5,197,676; 5,244,012; 5,249,748; 5,255,856; 5,273,072; 5,288,029; 5,288,525; 5,326,031; 5,340,289; 5,341,990; and, 5,364,035. The disclosures of these references also are hereby incorporated herein by reference. No representation is intended by this listing that this is a complete listing of all pertinent prior art, or that a thorough search of all pertinent prior art has been conducted, or that no better prior art exists. Nor should any such representation be inferred.
It has been found from experience gained from use of voltage blocks constructed as described in, for example, U.S. Pat. Nos. 5,632,816; 5,746,831; 5,787,928; and 5,944,045, that repeated arcing along the seats and ball surfaces of the four-way valves constructed as described in these patents can, in certain circumstances, result in erosion of the seat and ball surfaces. This erosion can lead to increased contamination of the solvent/voltage blocking medium with coating material. This, in turn, can lead to increased use not only of coating material but also of solvent/voltage blocking medium. Increased use of coating material equates with increased coating cost. Increased use of solvent/voltage blocking medium not only increases solvent/voltage blocking medium use and cost, but may also increase use of the molecular sieves used to extract the coating material vehicle from the solvent/voltage blocking medium, with its attendant cost. The impact of these increased usages also includes increased downtime to service systems of the type described in U.S. Pat. Nos. 5,632,816; 5,746,831; 5,787,928; and 5,944,045, in order to replenish their solvent/voltage blocking medium supplies and molecular sieves.